International Review of Hydrobiology最新文献

A key research aim for lotic ecosystems is the identification of natural and anthropogenic pressures that impact ecosystem status and functions. As a consequence of these perturbations, many lotic ecosystems are exposed to complex combinations of nonchemical and chemical stressors. These stressors comprise temperature fluctuations, flow alterations, elevated solute loads or xenobiotics, and all these factors can pose stress upon aquatic ecosystems on different temporal, spatial and biological scales. Factorial experiments are essential to reveal causal relationships especially between combined stressors and their effects in the environment. However, experimental tools that account for the complexity of running waters across different ecosystem compartments, levels of biological organisation, natural or anthropogenic environmental gradients, and replicability are rare. Here we present a new research infrastructure consisting of streamside mobile mesocosms (MOBICOS) that allows analysing the effects of stressors and stressor combinations through multifactorial experiments in near-natural settings and across anthropogenic pressure gradients. Consisting of eight container-based running water laboratories operated as bypasses to running surface waters, MOBICOS combines in situ real-time monitoring of physicochemical and biological parameters with manipulative experiments across ranges of environmental conditions. Different flume types can be set up within MOBICOS to separate and combine different ecosystem compartments (pelagic, epibenthic and hyporheic zones) in a flexible and modular way. Due to its compact design, the MOBICOS units can be shifted easily to particular sites of interest. Furthermore, simultaneous operation of multiple MOBICOS units at different sites allows the integration of natural gradients in multifactorial experiments. We highlight the versatility of the MOBICOS experimental infrastructure with two case studies addressing (a) hydraulic control of lotic biofilms and (b) pollution-induced community tolerance of biofilms along an environmental gradient. The modular and mobile MOBICOS units have the potential to significantly advance our understanding of causal relationships between natural environmental oscillations, anthropogenic stressors and their combined ecological impacts on lotic aquatic ecosystems beyond existing stream mesocosm approaches.

Urbanization is altering water quality and biotic communities of lake ecosystems worldwide, especially in developing regions. In this study, the diatom community structure and water quality of the epilimnion were analyzed in 38 lakes (40 sampling sites) in Wuhan City (central China) to assess the impacts of urbanization on lake ecosystems. Diatom communities displayed clear variation along the urban-to-rural gradient, with blooms of eutrophic species found in urban lakes in contrast to higher abundances of mesotrophic or oligotrophic taxa in rural lakes. Redundancy analyses revealed that the diatom community recognition to species, genus, and ecological guild level were all significantly correlated with Chl a, Si, and secchi depth, indicating that the changes in diatom communities were mainly explained by differences in nutrient concentrations and light condition. Considering the rapid urbanization and population expansion, it is important to carry out effective measures for the protection of these lake ecosystems, especially by reducing sewage discharge. The high consistency found between diatom community classification and water quality status highlights the applicability of diatoms for bioindication of shallow urban lakes, especially in rapidly developing cities. Even the taxonomic determination at the level of genera or ecological guilds can enable rapid water-quality assessment.

Aquatic communities across the Eurasian steppe face increasing anthropogenic pressures due to rapid population growth, catchment-wide land-use changes, and climate change. The particular type, intensity, overlay, and legacy of impacts along longitudinal gradients of Eurasian river networks provide a unique setting to investigate ecological responses in identifiable multiple stressor environments. We studied macroinvertebrate communities along the Kharaa River, Mongolia, which display a distinct, downstream gradient of moderate nutrient enrichment, disturbed bank morphology, reduced riparian vegetation, elevated turbidity, increased fine sediment substrate proportions, and fine sediment intrusion into the hyporheic zone. Within the encountered ranges of physical and chemical environmental factors (TP 0.02–0.09  mg/L, TN 0.33–0.96  mg/L, conductivity 167–322 µS/cm, formazin nephelometric units 0.62–5.43) and hyporheic fine sediment intrusion (0.9–1.6 g dry weight [DW]·L⁻¹·day⁻¹) the population densities and biomass of macroinvertebrates were high (5,313 ± 410 individuals/m² and 2,656 ± 152 mg DW/m²) and notably stable. In contrast, macroinvertebrate community structure showed strong and statistically significant negative linear relationships (Pearson's r) with turbidity, that is, for taxa richness (r = −.83), Shannon index of diversity (r = −.89), Evenness (r = −.86), the relative abundance of Ephemeroptera, Plecoptera, and Trichoptera (EPT) individuals (r = −.93) and relative biomass of hard substrate colonizers (r = −.86). The relative biomasses of fine substrate colonizers, as well as Chironomidae and Oligochaeta (both r = .76), were positively correlated with mean turbidity values. In addition, the Proportion of Sediment-sensitive Invertebrates (PSI) methodology was adjusted for local application and the resulting index scores followed a similar pattern, with PSI also being significantly correlated (r = .66) with the relative abundance of EPT individuals, the latter being the most sensitive macroinvertebrate community index. We conclude that fine sediment load is the key factor for shaping macroinvertebrate community structure in the multistressor setting of the Kharaa River followed by hydromorphological habitat complexity determined by shear stress, substrate, and grain size distributions. We suggest that the implementation of effective regional management strategies aiming at the reduction of fine sediment pollution should be given the highest priority.

Climate change may lead to increased droughts in the future, which in turn may lead to increased periods of stream drying. We conducted an experiment to test the effects of drying on fungal communities and microbial activity on decaying leaves from a stream. Our experimental setup included immersion of maple leaf cores for 2 weeks in a small stream to allow for the colonization of microbes. Leaves were then subjected for 2 weeks to four treatments: one control, where leaves stayed immersed in the stream, and three drying treatments in different settings (field, lab, and oven). Leaves were then returned to sterile water for 2 weeks of recovery. Microbial respiration declined after all drying treatments compared to the control, with the oven-dried leaves taking the longest time to recover. All drying treatments had similar respiration to each other and the control after 2 weeks of immersion recovery. Fungal communities on the leaves were assessed by polymerase chain reaction amplification of fungal DNA from leaves followed by denaturing gradient gel electrophoresis (DGGE). Most treatments had very similar communities based on phylotypes from DGGE, with little change during drying and recovery compared to immersion controls. However, the oven-dried leaves had a very different community developing during recovery. There were no differences in diversity or richness of DGGE phylotypes among treatments after recovery. Overall, the fungal communities, in our experiment, appeared resilient to the effects of short-term drying, with little change to community structure and relatively fast recovery in activity after rewetting.

Groundwater-dependent ecosystems are recognized as biodiversity hotspots, being, apart many negative human impacts, highly threatened also by ongoing climate warming. Clitellata (Annelida) are dominant invertebrates of permanent fauna in spring habitats, representing a heterogeneous group including both specialized cold-stenothermic and ubiquitous eurythermic species. Therefore, they seem to be a good model group to compare the effects of local springwater temperature (recorded in situ by data loggers) and mesoclimate (i.e., local) air temperature. By the analysis of clitellate assemblages at 41 isolated Western Carpathian spring fens, we found that their species composition was significantly driven by mesoclimate air temperature and springwater temperature independently of other important environmental variables (i.e., water mineralization, oxygen content, and total organic carbon). The effect of various environment-related and temperature-related variables on the number of clitellate species was analyzed separately for two categories, that is, substrate dwellers (endobenthic species) and surface-active (epibenthic) species. The decrease of the number of species with the increasing amount of inorganic particles <500 µm in substrate was observed in the substrate dwellers. Mesoclimate air temperature had no significant effect on the number of species of substrate dwellers. However, water temperature, specifically its daily fluctuation, turned out to have a strong effect. Only the sites with no or moderate fluctuation were inhabited by cold-stenotherm spring specialists and cold-water species. In contrast, no significant response to any temperature parameter was found for the number of surface-active species, which was driven only by other environmental variables. Our results suggest that climatically induced increase in temperature fluctuation of spring waters can result in notable reduction of cold-adapted clitellate species (mainly the family Lumbriculidae) at the expense of eurythermic species. Such a scenario predicts compositional changes leading to clitellate assemblages with a dominance of generalist and semi-aquatic species.

Mandarin fish Siniperca chuatsi is a widespread piscivorous species in lakes of the Yangtze River basin. However, their wild population has drastically declined, and survival and growth rates of stocked populations are low. Anthropogenic activities have reduced submersed vegetation and increased turbidity in lakes containing S. chuatsi, thus, we hypothesize that reduced submersed vegetation and increased turbidity could inhibit the feeding efficiency of juvenile S. chuatsi, subsequently reducing their growth and survival. To test this hypothesis, we experimentally examined the effects of a range of vegetation density and turbidity on predation of S. chuatsi. Laboratory predation trials were performed with a common prey fish Carassius auratus offered simultaneously to S. chuatsi in clear or turbid water under five different levels of vegetation density (0, 20, 40, 80, and 120 stems/m²). The total prey consumption per day (in 24 hr) by S. chuatsi on C. auratus was significantly affected by vegetation density, with the consumption positively linearly related with increased vegetation density. The total prey consumption was unaffected by turbidity. Prey size selection was not significantly influenced by vegetation density or turbidity. These results indicate that turbidity does not appear to negatively affect the predation of S. chuatsi, but a reduction of vegetation can negatively influence feeding induced by decreased predation efficiency, and hence might hinder survival and growth.

The Pampean region has become one of the most urbanised areas in South America with more than 91% of the Argentinean population. This region is ideal for human settlements that have historically chosen riverine grassland areas to settle. Consequently, urban streams are increasingly subjected to pressures affecting their functioning. The aim of this study was to assess urbanisation effects on two proxies of stream integrity: leaf litter decay and benthic invertebrate assemblage colonizing litter in streams draining urbanised versus reference grassland areas. We placed plastic coarse- and fine-mesh bags containing Populus nigra leaf litter along three urban and three reference reaches, and these were retrieved periodically to determine the remaining leaf mass and the identity and quantity of detritivore assemblage colonizing bags. The decay rate was negatively affected by urbanisation, and it followed a negative relationship with increasing Nitrogen concentration (mostly ammonia) and a hump-shape relationship against soluble reactive phosphorus. Urban invertebrate assemblages were significantly different from the reference reaches, and were species-poorer and characterized by tolerant taxa belonging to Naididae, Glossiphoniidae, and Nematoda, whereas Hyalellidae, Aeglidae, Chironomidae, Caenidae, Baetidae, and Hydrobiidae represented the reference reaches. Our proxies of structural (i.e., invertebrate assemblages) and functional (i.e., leaf litter breakdown) stream integrity were mostly driven by a nutrient-enrichment gradient and responded in a similar direction but with different magnitude to urban alterations.

The conversion of forests to agriculture in tropical areas profoundly changes adjacent streams by modifying hydrological conditions, altering light regimes, and increasing nutrient concentrations. In this study, we used an integrative approach to examine how transformations of intact forests affected the physical, chemical, and biological properties of periphyton, in three Brazilian Atlantic rainforest streams. We found that riparian land use change affected the stream periphyton in a variety of ways that were linked to the availability of light and nutrients. Periphyton standing stocks and accrual rates of new periphyton biomass on tiles were higher in deforested reaches than forested reaches. Linear mixed-model analyses showed that the increase of chlorophyll-a in the periphyton was explained by the increase in deforestation and soluble reactive phosphorus concentration. Deforestation also altered periphyton stoichiometry as deforested streams exhibited lower C:P, whereas C:N ratios decreased with increasing NH₄⁺ concentration that was higher in some deforested reaches. Periphyton productivity appeared to be limited by light in forested reaches and by nutrients in deforested reaches. There was differential availability of nitrogen and phosphorus in the deforested reaches, depending on land use type, and this resulted in different nutrient limitation. Periphyton community structure shifted from taxa less tolerant to high nutrients and light found in forested sites, to species tolerant to these conditions dominating periphyton assemblages in deforested sites. The loss of canopy cover was the strongest predictor of community composition for all sites, whereas phosphorus concentration was the best predictor of algal abundance in deforested reaches. This study highlights the complex effects of forest clearing on stream periphyton, ranging from changes to biomass accrual, nutrient limitation, stoichiometry, and community structure. We show the importance of using a comprehensive approach to help determine and predict how deforestation impacts stream ecosystems.